The present invention consists of an endovascular expander, of a non migrant positioning, and its purpose is to offer a means for positional self-fastening of said expander, preventing its dragging by the bloodstream.
Lately, in the field of medicine, endovascular treatments have had particular diffusion. These are characterized by being carried out through the interior of the lumen of the vessels, instead of entering through surgery, that is to say, making an incision in the tissues until reaching the artery or affected vein.
Such endovascular treatments are carried out in the lumen of the vessel, with various purposes and the employment of different means, either:
to produce the expansion of the artery or of the vein, PA1 dissolve thrombus in its interior, PA1 close abnormal communications of these vessels, among them or to the neighboring tissues, PA1 to cover the surface of the same with a prosthesis, as a means of "wrapping", PA1 return a dilated artery (aneurysm) to its normal caliber, PA1 isolate the internal surface of an artery from the physical or chemical elements of the blood, after accomplishing an expansion with a balloon ("internal bypass"); etc.
After American radiologist Charles Dotter researches, and within the endovascular techniques, the endovascular placement expanders has constituted an important advance, especially the elastic and permeable tubular structures that are normally known by their English denomination: "stents". So that, from here onwards and throughout this report they will be mentioned indistinctively as endovascular "expanders" or, simply, "stents".
The "stents"--generally structured in special metallic meshes--form very thin expansible pipes, generators of radial forces capable of maintaining the vessels open and in contraposition to the tensions that tend to close them.
In essence, it can be said that there exist three types of "vascular" stents: the thermosensitive ones, that adopt predetermined shapes at different temperatures, in particular that of the human body (as can be seen, for example, in the line Nitinol; in U.S. Pat. No. 4,425,908, etc.); the ones expansible with a balloon (as it is explained in European Patent EP 378.151); and the ones self-expansible through elasticity (as spread in U.S. Pat. No. 4,580,568).
The ""vascular" stents are being used for the treatment of angioplasties that turned out to be sub-optimum; to treat dissections after angioplasties and, lately, to assure endoluminal grafts, as well as acting as prosthesis for various applications, (Perrone, R and others, "Endoluminal prosthesis", Rev. Arg. de Cirugia", 1992; 62:146-149; Mazzariello, R.: "Applicacion percutanea de protesis biliares expandibles", in Revista Argentina de Cirugia, 1990: 979-983; etc.).
Also expanders and combined grafts have been used in numerous applications, such as: aneurysms, dissections, vascular trauma and arterial occlusion diseases.
Now then; one of the principal complications that result from the employment of the "Stent-graft" (expander graft) is the migration of the device, dragged by the own bloodstream. This occurs, for example, with the very thin "zigzag" wire pipes as the ones developed by Gianturco in 1985 and in the wire prosthesis of Mazzariello, (Rev. Arg. de Cirugia, 1990: 979-983), which by virtue of its particular structure scarcely frictioning, it is capable of being slid easily to a place not wished; being possible that this migration is tardily detected, even after its correct positioning.
To offset such problem, the fixing means of many expanders or "stents" is friction.
Also, and with the same anti-migrant purpose, many devices of the indicated type possess hooks or tabs added as a mechanism for the collaboration of subjection. J. F. Dumond, for example, developed a model to which it added external spicules of the same material of the prosthesis. (Dumond, J. F. "A dedicated tracheobrochial stent". Chest, 1990; 97-328-322), that had a limited diffusion, probably due to the problems observed upon intending to solve the sliding by means of rigid projections intended to be nailed in the walls of the vessel.
In effect; the drawback of using hooks, thorns or tabs is that many times the place of positioning of the arterial wall is found calcified and, therefore, it can not be penetrated. Thus, when the hook, the thorn or the tab is outside of the arterial wall--due to impossibility of penetrating it--a space is created between said wall and the expander, making possible the flow of blood out of the graft and thus, originating a peri-prosthesic loss.
In order to solve the outlined drawbacks, the inventor has developed an extra mechanism of subjection different from the hooks, tabs or rigid spicules, being stemmed from the observation of the scales that cover the body of the fish. In effect; when the hand is passed very gently throughout the surface of a fish, as long as the direction of the movement is in the direction sense of the scales, no resistance shall be found; but when the hand is moved in the opposite direction, resistance will be found.
Similarly, the new non-skid means--that collaborates to maintain the "stent" positioned in the correct place--does not act, unless it is and results necessary; in such case multiple plates that will be opposed shall be enabled, in fact, to the migrant displacement.
The important feature of the invention is that the presence of the cited plates, in essence, does not modify the form of the surface, since, practically, this surface results uniform and smooth.
Which implies an ingenious and simple solution to the outlined problems.